Many pieces of imaging apparatus currently on the market have an autofocus (hereinafter abbreviated as “AF”) for automatically adjusting a focus. A technique called TTL-AF (through-the-lens AF) is heavily used for this AF function at the present time. TTL-AF is a technique utilizing the fact that the edge of an image of the subject becomes clear at a focused focal point. Specifically, according to this technique, a specific frequency component of a predetermined area in a captured image (a preview image) is extracted, and an evaluation value which is an index showing the intensity of a contrast is determined from the thus extracted frequency component. The focus adjustment system lens is moved back and forth in such a way that the evaluation value fulfills a predetermined condition; e.g., the acquisition of the maximum value, thereby performing focusing operation.
However, the TTL-AF has a problem of being likely to focus on an object (or an area) exhibiting high contrast. For instance, under the situation called a night-view portrait in which the image of a person located at a comparatively-close position is captured while a night view is taken as a background, the night view serving as a background is likely to exhibit higher contrast than does the person that is the principal subject. In this case, the previously-described evaluation value is likely to become higher by bringing the night view into focus rather than bringing the person into focus. For this reason, there arises a problem of the night view remaining in focus; i.e., the imaging apparatus being likely to enter a so-called “rear-focused” state.
An AF technique utilizing information about a captured face has recently been put forward as AF means other than the TTL-AF technique. For instance, Japanese Patent Laid-Open Publication 2003-75717 describes a technique of: extracting the face of a person from a captured image (a preview image); estimating a distance to a subject from the size of the face; and performing focus adjustment operation. Japanese Patent Laid-Open Publication 2006-18246 describes a technique of: extracting a face of a person from a captured image (a preview image) or a distance between the eyes of the person; essentially estimating a distance to the subject from the size of the person or the distance between the eyes; and effecting TTL-AF in the vicinity of the thus-essentially-estimated distance to the subject. As mentioned above, attainment of a focus on an area other than the principal subject is prevented to a certain extent by utilization of information about the face of the person that is the principal subject for AF.
However, because suitable and unsuitable conditions are present for TTL-AF, suitable and unsuitable conditions exist for AF utilizing face information, as well. Consequently, as described in the Laid-Open Publications, there arises a case where an accurate focus adjustment operation cannot be performed under certain image-capturing conditions even when AF utilizing face information is adopted.